Goodman GMPO75-3 ser9911605881 . When warmed up runs OK . Cold the DI fan runs then HSI glows,gas valve opens and it lights with woof woof and goes out in 5 secs . Cycles again and it might start or go on third try. I polished the fire rod, set GV to 3.5 ins then changed GV. 24 volts at the GV .Shut off gas when running , it tries 3 times then red light blinks once.It just failed when warm and the circulating fan came on even though the gas was on for only 5 secs,it lit second try. I had a tech check it out and no solution.The furnace is a 1999 but new to me. Any ideas

Does the power drop off to the gas valve when running?

Hi. Furnace was warm and the voltage was between 24.4 & 24.8 at the gas valve the start up was smooth and quiet (no woof woof) I will let it cool and check it later tonight TNX davehs

Does the power drop off to the gas valve when running?

I would like to have a answer on this. Was the voltage being supplied to the gas valva when the burner stopped working? This is what should be checked.

Hi, my furnace usually fails when its coldat night after its been off. Since 5 pm it has lit first time and stayed on 4 times. I have a voltmeter connected and just have to be there when it fails , its so intermittent TNX davehs

Hi the 24volt went off at the gas valve and the flame quit. Then lit on second tryand ran fine. Ihad cooled the DI fan with an ice pack to simulate a cooled furnace. The fan spins freely with no noise, Could it be anything else?? TNX davehs

Try cleaning the flame sensor with steel wool. Sometimes if the sensor is a bit dirty it will not signal the circuit board that a flame is present and that will cause the furnace to shut down and retry.

Hi, Ialready polished the flame rod . I put a tach on the fan and its 3400 rpm? Should it not be 3000rpm or does that metter . davehs

Next step is to follow the control wires from the Gas valve back. If this has a power combustion blower there is usually a switch attached to it or a pressure switch of some type to prove its operation. Chech for the proper operation of that switch.